With advancements in computer technology, vehicles are becoming more and more computerized. Computerized vehicles are generally equipped with a plurality of electronic control units (ECUs). A program that is used by an ECU occasionally is rewritten to reflect a version upgrade or the like (see Japanese Laid-Open Patent Publication No. 2008-155892, hereinafter referred to as “JP2008-155892A”).
According to JP2008-155892A, it is judged whether or not a program can be rewritten based on a remaining stored energy level of a battery and a predicted value of an amount of consumed electric energy required to rewrite the program (see summary). More specifically, according to JP2008-155892A, the remaining stored energy level of the battery is calculated based on the present voltage and temperature of the battery. The predicted value of the amount of consumed electric energy is calculated based on a time and a current of the battery that are required to rewrite the program. It is then judged whether or not the program can be rewritten, based on whether or not the remaining stored energy level is greater than the predicted value of the amount of consumed electric energy (see FIGS. 5 and 6, and paragraphs [0025] and [0026]).